Hoses comprising a helically wound strip of convoluted material are known from U.S. Pat. Nos. 3,542,078; 4,167,645; and 4,224,965. Each of these references discloses a hose made by helically or spirally winding a strip of flexible material having a leading edge and a trailing edge such that the leading edge fits into a recess adjacent the trailing edge and the trailing edge fits into a recess adjacent the leading edge to form a convoluted structure. The helically wound strip results in a cylindrical configuration. Usually, an amount of adhesive material is used to bond the leading and trailing edge to each other so that the hose will not leak air or other fluid traveling through the hose.
The above-described hose construction is known as "spiral wound". Other constructions include pressure formed hoses. Spiral wound hoses exhibit certain benefits over pressure formed hoses, particularly by providing areas for flexation and areas for abrasion. Unfortunately, spiral wound hoses have exhibited problems in their manufacture and design. In particular, hoop strength, flexibility and bonding are all important features in a hose with a wide variety of applications. Unfortunately, a desirable balance between each of these characteristics has been difficult to achieve.
Hoop strength is determined by the rigidity of the material and the number of posts per foot extending radially from the centerline of the hose. The posts include any radially extending leading edge of the strip, any radially extending trailing edge of the strip, and any radially extending center walls of the strip. Because of limitations in machinery, bonding area, and product design, a desirable number of posts per foot has been difficult to achieve. Double construction hoses comprising two profiles of different materials have been developed to increase hoop strength. This double construction is costly, however, due to the fact that two strips must be extruded instead of one, and two profiles must be simultaneously wound.
Flexibility is determined by material type and flex of the profile design. Flexibility and hoop strength have always been inversely related to one another. Hoses with good hoop strength have exhibited poor flexibility, and vice versa. Hoses with a close pitch typically have good flexibility. However, in a hose with a close pitch it is difficult to control the weld position where adhesive or bonding material is applied.
Bonding of the leading and trailing portions of the profile has also been a problem with spiral wound hoses. The bonding material must stick to adjacent sides of the leading and trailing profile portions with enough adhesion to prevent peeling under conditions of stress during use. The bond must also be strong enough to resist separation due to temperature. To provide these features a large amount of weld has typically been used. A large amount of weld overcomes the peeling problem but generally flows into the flexation areas of the configuration and adversely limits the flexibility of the hose.
A need therefore exists for a hose construction having a cylindrical configuration and exhibiting good hoop strength, flexibility and bonding.